This invention relates generally to trailers towed by motor vehicles and more specifically to a universal trailer lighting adapter that operates to interface the lighting system of either American or foreign motor vehicles to a towed trailer. Trailers of the type manufactured in the United States utilize combined, rear-mounted turn/stop lamps to signal the intentions of the driver of the towing motor vehicle to drivers of vehicles following the towed vehicle. In addition, this type of trailer generally includes multiple running lights mounted at the rear and on the sides thereof to render the vehicle visible at night or in conditions of limited visibility.
In the case of American motor vehicles that are directly compatible with trailers also manufactured in the United States, it has been the practice in the prior art to wire the trailer lighting circuits directly to the corresponding individual motor vehicle lighting circuits. There are several disadvantages associated with this prior art practice. The most significant disadvantage is that the electrical load placed on the motor vehicle lighting circuits is at least doubled. This condition will usually cause both the trailer and motor vehicle lamps to operate at reduced brightness, causing a potential safety hazard. Since the lighting circuits of most motor vehicles are not designed to carry these increased electrical loads, components such as switches, turn signal flashers, wiring, and fuses are all prone to premature failure. This failure generally results in the potentially dangerous loss of lighting in both the motor vehicle and the trailer. At a minimum, it is necessary to replace the original motor vehicle directional signal flasher with a heavy duty flasher to carry the increased load presented by the trailer lights while maintaining the proper flash rate. In addition, trailer lighting systems are prone to develop electrical shorts due to wiring abrasion and lamp socket corrosion resulting from the presence of salt and moisture. Since the prior art generally teaches connection of trailer lighting systems directly to the motor vehicle lighting system wiring, such shorts will act to immediately disable both the trailer and motor vehicle lighting systems and may present a hazardous situation if undetected.
Most foreign motor vehicles, as well as some American models, utilize separate brake and directional signal circuits and are therefore not compatible with American trailers. Given this common situation, some type of adapter is required to convert the motor vehicle's three lighting signals (brake, left turn, and right turn) to the two signals (brake/left turn and brake/right turn) that are used by the trailer. The prior art practice in this situation is to wire the taillight circuit of the motor vehicle directly to the taillight or running light circuit of the trailer.
Prior art methods for adapting trailer lighting systems to motor vehicle lighting systems generally fall into two categories. The first category of devices uses electromechanical relays to convert motor vehicle lighting signals to signals that are compatible with the trailer. These devices are directed to the problem of adapting the turn/brake signal circuitry of imported motor vehicles to American trailers. They usually provide for isolation of the trailer brake/left turn and brake/right turn lamps from the lighting system of the motor vehicle by supplying power to these trailer lamps directly from the motor vehicle battery. However, the trailer running lamps are not so isolated in these prior art adapter devices. These prior art devices are sometimes separately fused to protect the motor vehicle lighting system from trailer shorts. The second category of prior art adapter devices employs solid state diode logic to adapt imported motor vehicles to American trailers. In this situation, the adapter device is powered directly by the motor vehicle brake and directional lighting circuits and does not provide any isolation or fusing to protect the motor vehicle lighting system from shorts that occur in the trailer lighting system. Neither of the above-described types of prior art adapter devices addresses the need for isolation of the trailer running lights from the motor vehicle lighting system or the need for isolating and fusing trailer lighting systems that are to be connected to American motor vehicles.
It is therefore the principal object of the present invention to provide a universal trailer lighting adapter that permits connection of the lighting systems of American trailers to either American or foreign motor vehicles. This and other objects are accomplished in accordance with the illustrated preferred embodiments of the present invention by providing circuitry that employs complementary metal oxide semiconductor (CMOS) logic elements in cooperation with solid state switches, resulting in negligible current drain, in the nanoampere range, from the motor vehicle battery when the motor vehicle is not in use. The circuitry is powered directly from the battery of the motor vehicle, thereby eliminating additional loading of the motor vehicle electrical components and wiring and assuring full brightness of lamps on both the motor vehicle and the trailer. A separate amplifier is provided for the running lights of the trailer. The circuitry is fused or current limited to protect the electrical systems of both the motor vehicle and trailer from trailer shorts that may occur. A light emitting diode is provided to indicate a malfunction in either the adapter circuitry or the trailer electrical system to the driver of the motor vehicle.